The present invention generally relates to a semiconductor integrated circuit device having an improved input/output interface circuit, and in particular to an input/output interface circuit which is designed to be subjected to a variety of tests with ease.
Generally, large scale integrated circuit devices (LSI devices) are subjected to a variety of tests in order to investigate whether or not LSI devices operate correctly. In test, LSI devices are activated under a specified operational condition, and it is investigated whether or not LSI devices operate without exhibiting abnormality. Functional test and DC characteristic test are typical of test of LSI devices. For example, in functional test, a predetermined pattern is supplied to an LSI device, and it is investigated whether or not a corresponding pattern is output from the LSI device. In direct current characteristic test (hereafter simply referred to as DC test), an external terminal other than an external terminal to be tested is set to a specified condition. In this state, a specified current is made applied or outputted to the external terminal to be tested. Then, the DC voltage of the external terminal to be tested is measured. Thereby, it is determined, based on the measured voltage, as to whether or not the LSI device can operate correctly in view of DC characteristics.
Generally, LSI devices includes external terminals, input/output circuits, and internal logic circuits. In conventional LSI device test, a signal applied to an external terminal other than an external terminal to be tested, passes through an input/output interface circuit, an internal logic, and input/output interface circuit. Then a signal responsive to the applied signal appears at the external terminal to be tested. That is, the applied signal such as a test pattern always passes through the internal logic circuit. For this reason, it is difficult to directly investigate the input/output interface circuit itself. In particular, it is very difficult to investigate that an input circuit which is a part of input/output interface circuits, operates correctly. Additionally, an external device which generates test patterns must be used in test. Moreover, it takes long to execute test programs to test LSI devices.